Descent with Modification: A Darwinian View of Life

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• Chapter 19
• Descent with Modification A
  Darwinian View of Life

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Evolution

• Evolution the change over time of the
  genetic composition of populations
• Natural selection populations of organisms can
  change over the generations if individuals having
  certain heritable traits leave more offspring
  than others (differential reproductive success)
• Evolutionary adaptations a prevalence of
  inherited characteristics that enhance organisms
  survival and reproduction

November 24, 1859
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Evolutionary history

• Linnaeus taxonomy
• Hutton gradualism
• Lamarck evolution
• Malthus populations
• Cuvier paleontology

• Lyell uniformitarianism
• Darwin evolution
• Mendel inheritance
• Wallace evolution

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Descent with Modification, I

• 5 observations
• 1- Exponential fertility
• 2- Stable population size
• 3- Limited resources
• 4- Individuals vary
• 5- Heritable variation

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Descent with Modification, II

• 3 Inferences
• 1- Struggle for existence
• 2- Non-random survival
• 3- Natural selection (differential success in
  reproduction)

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Evolution evidence Biogeography

• Geographical distribution of species
• Examples Islands vs. Mainland Australia Contin
  ents

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Evolution evidence The Fossil Record

• Succession of forms over time
• Transitional links
• Vertebrate descent

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Evolution evidence Comparative Anatomy

• Homologous structures (homology)
• Descent from a common ancestor
• Vestigial organs Ex whale/snake
  hindlimbs wings on flightless birds

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Evolution evidence Comparative Embryology

• Pharyngeal pouches, tails as embryos

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Evolution evidence Molecular Biology

• Similarities in DNA, proteins, genes, and gene
  products
• Common genetic code

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Final words...

• Absence of evidence is not evidence of absence.

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Phylogenetics - Chapter 20
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Phylogenetics

• The tracing of evolutionary relationships
  (phylogenetic tree)
• Whitaker System (K,P,C,O,F,G,S)
• Linnaeus
• Binomial Nomenclature
• Genus, specific epithet
• Homo sapiens
• Taxon (taxa)
• 3 Domains

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Phylogenetic Trees

• Cladistic Analysis taxonomic approach that
  classifies organisms according to the order in
  time at which branches arise along a phylogenetic
  tree (cladogram)
• Clade each evolutionary branch in a cladogram
• Types
• 1- Monophyletic single ancestor that gives rise
  to all species in that taxon and to no species in
  any other taxon legitimate cladogram
• 2- Polyphyletic members of a taxa are derived
  from 2 or more ancestral forms not common to all
  members does not meet cladistic criterion
• 3- Paraphyletic lacks the common ancestor that
  would unite the species does not meet cladistic
  criterion

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Constructing a Cladogram

• Sorting homology vs. analogy...
• Homology likenesses attributed to common
  ancestry
• Analogy likenesses attributed to similar
  ecological roles and natural selection
• Convergent evolution species from different
  evolutionary branches that resemble one another
  due to similar ecological roles

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A Cladogram
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• Chapter 21
• The Evolution of Populations

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Population genetics

• Population a localized group of individuals
  belonging to the same species
• Species a group of populations whose
  individuals have the potential to interbreed and
  produce fertile offspring
• Gene pool the total aggregate of genes in a
  population at any one time
• Population genetics the study of genetic
  changes in populations
• Modern synthesis/neo-Darwinism
• Individuals are selected, but populations
  evolve.

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Hardy-Weinberg Theorem

• Serves as a model for the genetic structure of a
  nonevolving population (equilibrium)
• 5 conditions
• 1- Very large population size
• 2- No migration
• 3- No net mutations
• 4- Random mating
• 5- No natural selection

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Hardy-Weinberg Equation

• pfrequency of one allele (A) qfrequency of
  the other allele (a) pq1.0
  (p1-q q1-p)
• P2frequency of AA genotype 2pqfrequency of
  Aa plus aA genotype q2frequency of aa
  genotype
  p2 2pq q2 1.0

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Microevolution, I

• A change in the gene pool of a population over a
  succession of generations
• 1- Genetic drift changes in the gene pool of a
  small population due to chance (usually reduces
  genetic variability)

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Microevolution, II

• The Bottleneck Effect type of genetic drift
  resulting from a reduction in population (natural
  disaster) such that the surviving population is
  no longer genetically representative of the
  original population

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Microevolution, III

• Founder Effect a cause of genetic
  drift attributable to colonization by a limited
  number of individuals from a parent population

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Microevolution, IV

• 2- Gene Flow genetic exchange due to the
  migration of fertile individuals or gametes
  between populations (reduces differences between
  populations)

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Microevolution, V

• 3- Mutations a change in an
  organisms DNA (gametes many generations)
  original source of genetic variation (raw
  material for natural selection)

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Microevolution, VI

• 4- Nonrandom mating
• Courtship, Ultimate and Proximate Causations of
  Attraction
• inbreeding and assortive mating (both shift
  frequencies of different genotypes)

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Microevolution, VII

• 5- Natural Selection differential success in
  reproduction only form of
  microevolution that adapts a population to its
  environment

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Population variation

• Polymorphism coexistence of 2 or more distinct
  forms of individuals (morphs) within the same
  population
• Geographical variation differences in genetic
  structure between populations (cline)

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Variation preservation

• Prevention of natural selections reduction of
  variation
• Diploidy 2nd set of
  chromosomes hides variation in the heterozygote
• Balanced polymorphism 1-
  heterozygote advantage (hybrid vigor i.e.,
  malaria/sickle-cell anemia)
  2- frequency dependent
  selection (survival reproduction of any 1 morph
  declines if it becomes too common i.e.,
  parasite/host)

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Natural selection

• Fitness contribution an individual makes to the
  gene pool of the next generation
• 3 types
• A. Directional
• B. Diversifying
• C. Stabilizing

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Sexual selection

• Sexual dimorphism secondary sex characteristic
  distinction
• Sexual selection selection towards secondary
  sex characteristics that leads to sexual
  dimorphism

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• Chapter 22
• The Origin of Species

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Macroevolution the origin of new taxonomic groups

• Speciation the origin of new species
• 1- Anagenesis (phyletic evolution) accumulation
  of heritable changes
• 2- Cladogenesis (branching evolution) budding
  of new species from a parent species that
  continues to exist (basis of biological diversity)

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What is a species?

• Biological species concept (Mayr) a population
  or group of populations whose members have the
  potential to interbreed and produce viable,
  fertile offspring (genetic exchange is possible
  and that is genetically isolated from other
  populations)

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Reproductive Isolation (isolation of gene pools),
I

• Prezygotic barriers impede mating between
  species or hinder the fertilization of the ova
• Habitat (snakes water/terrestrial)
• Behavioral (fireflies mate signaling)
• Temporal (salmon seasonal mating)
• Mechanical (flowers pollination anatomy)
• Gametic (frogs egg coat receptors)

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Reproductive Isolation, II

• Postzygotic barriers fertilization occurs, but
  the hybrid zygote does not develop into a viable,
  fertile adult
• Reduced hybrid viability (frogs zygotes fail to
  develop or reach sexual maturity)
• Reduced hybrid fertility (mule horse x donkey
  cannot backbreed)
• Hybrid breakdown (cotton 2nd generation hybrids
  are sterile)

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Modes of speciation (based on how
gene flow is interrupted)

• Allopatric populations segregated by a
  geographical barrier can result in adaptive
  radiation (island species)
• Sympatric reproductively isolated subpopulation
  in the midst of its parent population (change in
  genome) polyploidy in plants cichlid fishes

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Punctuated equilibria

• Tempo of speciation gradual vs. punctuated
  equilibrium (divergence in rapid bursts) Niles
  Eldredge and Stephen Jay Gould (1972) helped
  explain the non-gradual appearance of species in
  the fossil record

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• Chapter 20 and 23
• Phylogeny Systematics

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Phylogeny the evolutionary history of a species

• Systematics the study of biological
  diversity in an evolutionary context
• The fossil record the ordered array of
  fossils, within layers, or strata, of
  sedimentary rock
• Paleontologists

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The fossil record

• Sedimentary rock rock formed from sand and mud
  that once settled on the bottom of seas, lakes,
  and marshes
• Dating
• 1- Relative geologic time scale sequence of
  species
• 2- Absolute radiometric dating age using
  half-lives of radioactive isotopes

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The Geological Time Scale
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Biogeography the study of the past and present
distribution of species

• Pangaea-250 mya v Permian extinction
• Geographic isolation-180 mya v African/South
  American reptile fossil similarities v
  Australian marsupials

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Mass extinction

• Permian
• (250 million years ago) 90 of marine animals
  Pangea merge
• Cretaceous
• (65 million years ago) death of dinosaurs, 50
  of marine species low angle comet

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Endosymbiotic Cell Theory